Wire bonding apparatus with a textured capillary surface enabling high-speed wedge bonding of wire bonds

ABSTRACT

Methods and systems are described for enabling the efficient fabrication of wedge-bonding of integrated circuit systems and electronic systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S.application Ser. No. 12/851,981, entitled “Wire Bonding Method andDevice Enabling High-Speed Wedge Bonding of Wire Bonds” filed on Aug. 6,2010, which is hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present invention relates generally to semiconductor devicepackaging and interconnection technologies. In particular wedge bondingtechnologies are discussed. More particularly, apparatus, methods,software, hardware, and systems are described for achieving high-speedwedge bonding of wire bonds.

BACKGROUND OF THE INVENTION

In the field of semiconductor packaging, wire bonding can be used tointerconnect integrated circuits and other associated componentstogether. In particular, two main modes of wire bonding are in commonusage. Ball bonding and wedge bonding. Both methods are well known inthe art and have been in use for many years. As is known, ball bondingis commonly known and is frequently used with gold materials. Howevergold is relatively expensive. Additionally, such gold ball bondingrequires surface plating (for example using silver) and heat to maintaingood adhesion to bond pad materials. Additionally, attempts have beenmade to use ball bonding with copper materials. However, at the hightemperatures required for copper ball formation oxide formation is acommon problem. The problem is quite pronounced as copper oxides areinsulating materials that have proven difficult to bond. Additionally,deformation of the electrical connections made at high temperatures leadto reliability issues. Methods of avoiding oxide formation require theuse of oxygen free ambient conditions. This comes with its own set ofproblems. Similar oxide formation issues make aluminum a difficultmaterial for ball bonding applications as well. An advantage to ballbonding is its high rate of processing speed. In many applications,average bonding speeds of the order of 12-14 bonds per second can beattained.

However, because some materials are difficult to work with using hightemperature ball bonding, an alternative wedge bonding approach can beused. A disadvantage of such prior art wedge bonding technique is thatit is a comparatively slow process with average bonding speeds of theorder of 2-3 bonds per second being common.

Moreover, although ball bonding and wedge bonding have been used in theindustry for many years, wedge bonding has up until this point been arelatively slow process even after 30 years of use. Accordingly, ways ofimproving wedge bonding speeds would be advantageous. Thus, whileexisting systems and methods work well for many applications, there isan increasing demand for wedge bonding methodologies that enableincreased speed using a variety of materials including aluminum. Thisdisclosure addresses some of those needs.

SUMMARY OF THE INVENTION

In a first aspect, an embodiment of the invention describes method forhigh-speed wired bonding. The method involves positioning a distal endof a wire-bonding capillary near a first bonding site. Extruding alength of bonding wire from an aperture in the end of the capillary.Imposing a movable deflector against the extruded length of bonding wireto bend the bonding wire to form a bent portion at an end of the bondingwire. Moving the bent portion of the bonding wire into contact withfirst bonding site. Wedge bonding the bent portion of the bonding wirewith the first bonding site. In one approach, the wedge bonding cancomprise, compressing and/or ultra-sonic bonding the bent portion of thebonding wire between the bonding site and a facing surface of thecapillary and ultrasonically bonding the bent portion of the bondingwire to the first bonding site. To further continue an example method,the capillary can be moved away from the first bonding site toward asecond bonding site where another end of the bonding wire is wedgebonded to the second bonding site to establish a wire bond connectionbetween the first and second bonding sites.

In another aspect, embodiments of the invention include a wire bondingapparatus comprising a support for holding wire bonding substrates, awire bonding capillary with an aperture for carrying and extruding bondwire and enabling bond wire attachment to wire bonding substrates, amovable deflector element arranged to enable movement of the deflectorelement to bend an extruded length of bonding wire such that the bentextruded length of bonding wire can be articulated at different bondline angles while maintaining a constant rotational orientation for thecapillary, and a controller configured to enable control the operationof the wire bonding apparatus.

In another aspect, embodiments of the invention describe a movabledeflector element module for use in wire bonding operations. One suchmodule includes a deflection member configured to enable movement in anx axis and y axis direction. The member includes an aperture oriented ina z-axis with the aperture having inner wall that defines a wire contactsurface having a plurality of wire guide features. Also, a deflectionactuator is configured to move the deflection member in said x and yaxis directions as directed by a control element configured to specify xand y axis movement for the deflection actuator.

In another aspect, embodiments of the invention describe a capillaryelement for use in high speed wire bonding operations. One suchcapillary comprises a capillary including a facing surface at a tip endof the capillary. Also including an aperture that penetrates through thecapillary to an opening in the facing surface of the shaft to enable abond wire to pass through the aperture exiting the opening in the facingsurface. The facing surface defines a substantially ring-shapedroughened surface area with a substantially flat surface angled in arange of about 0° to about 4°.

General aspects of the invention include, but are not limited tomethods, systems, apparatus, and computer program products for enablingimproved high speed wedge bonding of wire bonds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIGS. 1( a) and 1(b) are views of a prior art wedge bonding bond head asshown in side and top section view.

FIG. 1( c) is a top down diagrammatic view of a prior art bonding toolshowing the changing rotational orientation of the wedge bonding tool asit progresses around a die forming a series of wire bonds.

FIG. 2 is a block diagram illustrating an example wedge bondingapparatus in accordance with the principles of the present invention.

FIG. 3( a) is a block diagram illustrating an operational relationshipbetween an inventive deflector element and associated actuator elementin a deflector module in accordance with the principles of the presentinvention.

FIG. 3( b) is illustration of a specific embodiment of a deflectormodule in accordance with the principles of the present invention.

FIGS. 3( c)-3(e) are a set of illustrations depicting a methodembodiment of using selected embodiments of a deflector module toposition and deflect a wire bond wire in accordance with the principlesof the present invention.

FIGS. 4( a)-4(g) are a set of illustrations illustrating one exampleprocess embodiment of using a wedge bonding tool in accordance with theprinciples of the present invention in conjunction with a deflectorelement to form directional wire bonds used for connecting IC elementswith external connectors such a lead frames.

FIG. 4( h) shows an example of a bond angle and an alignment approachfor one embodiment of wedge bonding in accordance with the principles ofthe invention.

FIGS. 5( a) and 5(b) show an example embodiment of deflector element andaperture in accord with one example embodiment of the invention.

FIG. 6 is a flow diagram illustrating one approach to implementing wedgebonding in accordance with the principles of the invention.

FIGS. 7( a)-7(d) illustrate some aspects of one embodiment of a wedgebonding capillary suitable for employment in accordance with theprinciples of the invention.

In the drawings, like reference numerals are sometimes used to designatelike structural elements. It should also be appreciated that thedepictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is made to particular embodiments of the invention. Examplesof which are illustrated in the accompanying drawings. While theinvention will be described in conjunction with particular embodiments,it will be understood that it is not intended to limit the invention tothe described embodiments. To contrary, the disclosure is intended toextend to cover alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

Aspects of the invention pertain to methods and apparatus for enablinghigh speed wedge bonding in semiconductor wire bonding applications.

The diagrammatic illustrations of FIGS. 1( a)-1(c) provide anunderstanding of some of the problems inherent in state of the art wedgebonding technologies. FIG. 1( a) is a diagrammatic side view of aportion of a wedge bonding tool 100. A bond head 101 feeds a bondingwire 102 downward and can use a guide 103 to help position the wire 102in desired proximity to a bond pad 104. When the bond head 101 is movedin a direction toward the bond pad 104 and downward pressure is appliedagainst the bond pad 104 and the wire 102 and typically ultrasonicenergy is applied to the wire 102 to bond the wire 102 to the pad 104.The tool 100 lifts the bond head 101 and moves it to an associated lead(or other bonding site) that is to be connected with the bond pad 104 bya wire bond. The wire is then typically broken off to complete the wirebond between the two bonding pads.

FIGS. 1( a) and 1(b) illustrate a facing surface 101 f of the bond head101. FIG. 1( b) is a top down section view of the bond head 101 of FIG.1( a). The wire 102 runs under the bond head 101. In particular, thisview shows that during wedge bonding the head move 105 in a directiontoward the eventual other end of the wire bond connection (i.e., theother bonding surface). Thus, the motion of the wire and head isessentially a straight line motion between the first bonding site andthe target bonding site.

As shown in FIG. 1( c), it is this straight line motion betweenbeginning bond pad bonding site and target bond location that defines a“bond line” between the two locations. FIG. 1( c) presents a simplifiedtop down view of an integrated circuit die 110 and bond connections toexternal contacts. As shown here the die 110 includes a plurality ofbond pads 111 arranged around a top surface of the die 110. Also shownare a few of the many electrical connectors (112-114) arranged aroundthe circumference of the die 110.

In examining a first wire bond connection 122 connecting one of the pads111 with a first external connector 112 the wire bond 122 defines a bondline between the two contact locations. Here we arbitrarily identify thebond line 122 as having angle of 0°. The diagrammatic illustrationincludes a first bubble 131 that shows a top down view of the associatedbond head 101 and the bond wire 102. During wedge bonding, the bond headis moved in direction 141 from the bond pad 111 toward the final bondingsite at connector 112. In the wedge bonding process, this process isrepeated for each pair of pads and contact for the die 110. Thus, thebonding proceeds around the circumference of the die until completed.

For example, as the process has moved clockwise around the die anotherwire bond 123 is briefly discussed. A second external bond site 113 iswire bonded with an associated one of the pads 111 thereby defining thewire bond 123 and its associated bond line. With reference to the firstbond line (122) it is shown that the bond angle has changed. Here thatangle change 135 is represented as 90°. Thus the bond line 123 lies at90° from the first bond line 122. This has consequences in how the wirebond is formed. The diagrammatic illustration includes a second bubble132 that shows a top down view of the associated of the same bond head101 and a bond wire 102. Because the bond line is significantly changed,the rotational orientation of the bond head 101 must also significantlyrotate. This rotation enables wedge bonding between the external bondsite 113 and its associated bond pad. During wedge bonding, the bondhead 101 is moved in second direction 142 from the bond pad 111 towardthe final bonding site at connector 113.

Likewise, as the process continues moving clockwise around the dieanother wire bond 124 is briefly discussed. Here, an example thirdexternal bond site 114 is shown wire bonded with an associated one ofthe pads 111 thereby defining the wire bond 124 and its associated bondline. With reference the to the first bond line (122), it is shown herethat the bond angle 136 has further to about 120°. Thus the bond line124 lies at 90° from the first bond line 122. Again, this hasconsequences in how the wire bond is formed. The diagrammaticillustration includes a third bubble 133 that shows a top down view ofthe associated of the same bond head 101 and a bond wire 102. Becausethe bond line is again significantly changed, the rotational orientationof the bond head 101 must also significantly rotate. At this point therotation is about 120 degrees. Also, as before, this rotation enableswedge bonding between the external bond site 114 and its associated bondpad. During wedge bonding, the bond head 101 is moved in third direction143 from the bond pad 111 toward the final bonding site at connector114. And so it continues until the die 110 is completely bonded.

It is very important to consider that the bond head 101 realignmentprocess takes a considerable amount of time. In fact, it is whataccounts for the majority of the disparity in bond rates between theball bonding process (e.g., about 14 bonds/s) and the prior art wedgebonding process (e.g., about 2-3 bonds/s). Accordingly, an approach forremoving this step from the process has considerable advantage in awedge bonding process.

Accordingly, FIG. 2 is a block diagram describing a novel wedge bondingapparatus 200 in accordance with one embodiment of the invention.Several of the many listed components are optional or can be substitutedfor other elements. The apparatus includes a wedge bonding module 210arranged to enable wedge bonding of an IC chip 202 to another substrateduring a wedge bonding process. The wedge bonding module includes acontrol arm 211, an associated wire bonding capillary 213, and adeflector module 220 arranged to enable deflection of a portion ofsupplied by a capillary 213 as needed. The wedge bonding device 200typically includes a control module 230 configured to run software andchange operating conditions and parameters prior to and during use. Theapparatus can also include a viewing station 204 that enables viewingand can be used to assist in adjusting, and positioning of bondingmodule 210.

The wedge bonding module 210 typically includes a control arm 211 thatcan include an ultrasonic head (not shown in this view) with a capillary213 used as a bonding tool mounted on a distal end thereon. The module210 can include a linear motor (not shown) that drives the capillary 213and bonding arm 211 (as can optionally move the deflector module 220) inthe vertical direction, that is, in the Z-direction. The linear motor isbut one of many examples of a suitable motive device that can be used toaccomplish the desired movement in the module 210. This Z-axis movementenables the bond tool 213 to apply wire to various locations on thesubstrate 202. An XY table 214 is used as an XY positioning unit thatholds the bonding module 210 (including control arm 211, bondingcapillary 213, deflector module 220, and image pickup unit 204) andmoves the module two-dimensionally a substantially horizontally arrangedX-direction and Y-direction, and positions the same capillary 213 forwire bonding.

The control module 230 can include one or more microprocessors forcontrolling the entire wire bonding apparatus 210. For example, a drivedevice 231 can provide control signals to the bonding head 213 and theXY table 214 in response to a command signal from a controller 232.Commonly, software (or firmware) is executed on a microprocessor of thecontroller 232 and the operation of wire bonding or the like isperformed by implementing the program. A support 205 holds the IC device202 so that it can be wire bonded to another substrate. In this depictedembodiment, the other substrate comprises a lead frame 203.Additionally, in some embodiments, the support can include a heaterunit. In one implementation, the semiconductor chip 202 is mounted on alead frame 203 which can be mounted on the heater plate of a heater unitat the top of the support 205. The lead frame 203 can be heated by theheater unit.

Also, the wire bonding apparatus 200 typically includes an operationpanel 233 having, for example, data input features that can include, butare not limited to track balls, alphanumeric value entering keys, andoperating switches for enabling input and output of data such as processparameters and further display of the data for operation of the device200. Such data can be input into the controller 232 to, for exampleusing a track ball, enable manual movement of the XY table 214. Thecontrol unit 232 and the operation panel 233 are collectively referredto as an operating unit, hereinafter. The wire bonding apparatus 200 canbe operated manually or automatically by the operation of the operatingunit.

The wedge bonding module 210 which drives the bonding arm 211 verticallyin the Z-direction includes a position detection sensor 216 fordetecting the position of the bonding arm 211, and the positiondetection sensor 216 is adapted to output the position of the capillary213 mounted to the distal end of the bonding arm 211 from the positionof a preset original point of the bonding arm 211 to the control device232. The linear motor of the wedge bonding module 210 drives the bondingarm vertically in response to instructions from the controller 232 whichalso controls the magnitude and the duration of a load to be applied tothe capillary 211 at the time of bonding.

Additionally, an ultrasonic oscillator (not shown) can be located withinthe arm 211 which, in one embodiment, can use a piezoelectric transducerto cause the capillary 213 to generate the requisite ultrasonicoscillations that can be applied to the capillary 213, for example, uponreception of a control signal from the controller 232.

Additionally, the controller 232 provides signals to the deflectormodule 220 that enable it to deflect wire extruded from the capillary213 in accord with certain aspects of the invention. This will bediscussed in greater detail in the following paragraphs.

In general, the wire bonding apparatus 200 is configured to connect bondpads of the IC device 202 to external bonding sites, for example,bonding sites on a lead frame 203. These bond connections are made usingbond wire such as aluminum wire. Also, gold and copper can be used inaccord with this invention. Aluminum being attractive because it is asofter material than both copper and gold thus reducing stress on theunderlying substrate (the die 202) during wedge bonding. The approachdisclosed in this application has several advantages over prior artmethods. Unlike ball bonding, the present invention can be practiced atroom temperature thus removing a large array of heat related problemsfrom the system. Additionally, the need for non-oxygen ambient is alsoremoved from the system. Also, it provides a high-speed method forachieving wedge bonding which has been a slow process for over 30 years.Thus, this invention meets a long unmet need and is particularlyadvantageous when used with materials like aluminum bonding wires.

A novel feature of the invention includes a deflector element 220 whichis position in an operational arrangement with a bonding capillary 213.Typically, but not exclusively, the deflector element 220 is mountedwith the bonding arm 211. The deflector element 220 comprises a movabledeflector member and an associated actuator that enables controlledmotion for the movable deflector member. The motion of the movabledeflector member is intended to execute x-axis and y-axis movement andbending of an extruded portion of a bond wire extending from a capillary213.

In general, the deflector element 220 and capillary 213 are controlledby software and hardware enabling their integrated operation with thewire bonding recipe of the bonding processes executed by the apparatus200.

Such a movable deflector member can comprise one or more separateelements configured alone or in combination to enable such x, y movementand bending in a bond wire. The actuator can comprise a drive motor(s),magnetic actuators, and other motive elements. FIG. 3( a) is a blockdiagram schematically illustrating an embodiment of a deflector element220. In particular there is a movable deflector member 301 and anassociated actuator system 302.

FIG. 3( b) is a diagrammatic depiction schematically illustrating anembodiment of a deflector element 220. In particular there is a movabledeflector member 311 and an associated actuator system 312. In thisparticular embodiment, the member 311 includes an aperture 313 used tomanipulate the position of the bond wire. In such case the bond wire isdeflected by the inner surfaces of the aperture 313. For example, theaperture 313 is made in a working end of a deflector wand 311 thatincludes an arm portion 311 a used to engage the working end with theactuator 312. The actuator system can comprise any system of motivedevices suitable for moving the deflector member (or wand) 311 in thedesired directions.

FIGS. 3( c) & 3(d) are diagrammatic depictions of the deflector member311 embodiment such as shown in FIG. 3( b). The aperture 313 has adiameter that is greater than a diameter of an associated capillary 213.One example of a set of ranges for capillary outer diameter is on theorder of about 2-100 mils. Such ranges are very flexible and dependlargely on the size of the bonding wires and bonding pads (or othercontacts) used. A complementary aperture 313 has a larger aperture. Inone embodiment, the aperture can range from about 10-25% larger than thecapillary diameter. For example, an aperture diameter for a 10 mildiameter capillary is on the order of about 11-13 mils. In one example,a capillary has an outer diameter of about 30 mils, with an associateddeflector inner diameter of about 40 mils. Referring back to FIG. 3( b),in one example the thickness of the deflector 311 can be on the order ofabout 4-30 mils. It should be specifically pointed out that althoughspecific dimensions are identified, a considerably larger range ofdimensions, shapes, and configurations are expressly contemplated bythis patent. Additionally, such deflector members can be made using anumber of different materials or combinations of materials. In oneexample, the deflector member 311 can be made of a tungsten material.

FIG. 3( d) is a bottom up view of an example embodiment. The aperture313 of the deflector member 311 includes an inner surface 313 d that canoperatively deflect the bond wire 314. Also, the cross-section 315 ofFIG. 3( d) is used to describe the process illustrated in FIG. 4.

FIG. 3( e) is a simplified view (as in FIG. 3( d)) of an exampleembodiment showing deflection of a wire 314. The deflector member 311moves in an arbitrary direction 316, shown here as having an x-componentand a y-component. Importantly, the wire 314 is deflected by a surfaceof the inner wall of the aperture 313 d. Thus, the wire 314 is bent andorient in a desired direction. Importantly, the orientation of thecapillary 213 does not change (in an x, y direction) to accommodatechanging angles of the bent bond wire. The capillary 213 maintains thesame orientation regardless of bond angle (or wire angle) in the bentbonding wire.

It is particularly pointed out that the deflection of the wire 314 isachieved by the relative motion of the wire with respect to thedeflector 311. In other words, it can be that the capillary 213 itselfis moved relative to a stationary deflector 311.

FIGS. 4( a)-4(g) illustrate an implementation of a process used toestablish a high speed wedge bond.

FIG. 4( a) shows a capillary 213 in position above a bond pad 401preparatory to bonding a wire 314 to the pad. This view is similar tothe cross-section axis 315 shown in FIG. 3( d). In this embodiment, adeflector member 311 is in position to deflect an extruded portion 314 eof a bonding wire 314 extending from a capillary.

In one feature of the invention, the facing surface of the capillary 317is a substantially flat surface. The surface 317 generally having a faceangle of in the range of about 0-4°. This is important because it isdesirable to have the greatest amount of surface area of the facingsurface applied against a bend bonding wire.

In describing the process, the capillary 213 is positioned above thedesired bonding site 401, a portion of wire 314 e is extruded from thewire in a desired length. For example, the length 314 e is on the orderof a radius of a flat facing surface 317 of the capillary. For example,using an 8 mil diameter capillary, the extruded portion 314 e can be onthe order of about 3-4 mils in length. The bonding wire can be made ofany material and any thickness. Gold, copper, aluminum, and allots ofthe same provide some examples of suitable materials. Such wires are onthe order of 15 μm-to 2 mil as well as other thicknesses. In oneexample, a capillary 213 extrudes a portion of a bond wire 314 e adesired length through the aperture 313 and then fixed in length. Forexample, the wire can be extruded through an open wire clamp to thedesired length, then the wire clamp fixes the wire in place (stabilizingthe length) and then relative movement of the deflector and capillarybend the wire as appropriate.

The bond angle required to connect the bond pad 401 to a desiredexternal bonding site is determined. This enables the correct x, ydeflection to be applied to the bent portion of the wire 403. Then, asshown in FIG. 4( b), the deflector 311 is moved in direction 402 thatbends the extruded wire portion 314 e in the desired direction to form abent wire portion 403 oriented in a desired direction.

After bending, as shown in FIG. 4( c), the deflector 311 is moved back404 into a centered position (centered on the capillary 213).

Then, as shown in FIG. 4( d), the capillary 213 is stamped downward 405into the bonding site 401 such that the bent wire 403 is compressed(See, FIG. 4( e)) between the facing surface 317 of the capillary 213and the surface of the bond pad 401. One advantage of using aluminumwire is that aluminum is softer than gold and copper. Relative to gold,this means that the downward force applied to an aluminum wire and bondpad 401 is less than half the pressure applied to a similar diametergold wire. This places a good deal less stress on the underlyingsemiconductor device. This lack of stress is particularly advantageousin that it substantially reduces stress induced damage in the underlyingdevices.

Thus, as is shown in FIG. 4( e) the stamping process compresses the bentportion of bond wire. Additionally, to establish a solid bond ultrasonicenergy is applied to the wire to ultrasonically bond 314 b the wire tothe bond pad 401.

Once bonded, as shown in FIG. 4( f), the wire 314 is lifted away fromthe wedge bond 314 b and moved to the complementary bonding site (e.g.,on an associated lead frame). Once, the capillary is moved to thecomplementary bonding site a second wedge bond is made and then the wire314 is broken off. The capillary 213 is retracted back upward throughthe deflector aperture 313 (See, FIG. 4( g)). The capillary is alsomoved to a next bond pad and a new length of wire 314 e is extruded forbonding to the second bond pad. The illustrated process is repeatedagain and again until a desired number of wire bonds are made with thedie substrate.

Additionally, when the wire portion 403 (314 e) is bent in direction 402(See, e.g., FIG. 4( b)) the direction of deflector 311 movement 402 isgenerally aligned to facilitate a direct connection between the subjectbond site (bond pad 401) and the desired target bond site (e.g., thelead frame attachment point). For example, with reference to FIG. 4( h)a bond pad 111 is positioned in an example arrangement with anassociated connector 115 (e.g., a portion of a lead frame) onto which asecond bond site is located and a second wire bond is to be made. A bondwire 116 is bent in an appropriate direction (as shown) generallyaligned with a direct line to the second bond site 115. The bond angle117 can change for each wire bond connection between first site (e.g.,111) and second associated bond site (e.g., 115) as a wire bondingprocess is executed around an integrated circuit die. The methods anddevices described herein are flexible and robust enabling a 360° changein bond angles. Advantageously, the disclosed embodiments do not requireany change in rotational bond head configuration as the process proceedsaround the circumference of the die. This allows the process to continuewith no rotational adjustment of the bond head (the capillary) as itmoves from wire bond to wire bond to wire bond. This eliminates theconstant readjustments required of prior art wedge bonding tools as theymove from wire bond to wire bond. Thus, it is far faster than thesetools, having bond rate similar to that of ball bonding tools andprocesses. This has been a major jump forward solving a 30 year oldproblem and will likely find broad wedge bonding application across theentire semiconductor industry.

It is pointed out that the wire can be positioned and held in placeusing standard clamp and wire tensioners as can be found in ball bondingtools. The clamp holds the wire in place while the deflector bends thewire into the desired configuration and then releases the wire once itis positioned at the desired bonding site. Moreover, in some embodimentsthe wire tensioner (or other associated vacuum systems) can be dispensedwith altogether.

FIG. 5( a) shows another embodiment of a deflector aperture. In thisdepiction, a deflector arm 511 a supports a working end 512 of adeflector element 511. In particular, a different embodiment of apertureis shown. The aperture 513 comprises a flower-shaped aperture 513arranged with a plurality of wire guiding features 514. The innersurface of the aperture 513 is shaped generally like a “flower” havingpetal portions. These petal portions 514 are the guide features 514.They are arranged such that when the aperture is moved across (402) theextruded wire (e.g., 314 e) the wire can be generally centered at anadir 515 of one of the features 514. Importantly, the presence ofapexes 516 between the petals can prevent the wire from deviating fromone petal to another as the deflector moves across the capillary. Asshown in this embodiment, the aperture 513 includes 8 “petals” thatserve as the guide features 514. Different embodiments can, of course,have more or fewer petals. Also, a wide range of petal shapes orconfigurations can be employed as might be suggested to one of ordinaryskill by this disclosure.

An example depiction of the operation of a guide feature 514 is shownwith reference to FIG. 5( b) which shows a portion of an aperture of onepossible embodiment of a deflector element 511. As shown here each ofthe petals 514 has a curvature defining a nadir 515 portion located atthe sidewall of the aperture 513 for each petal 514. Moreover,separations between petals 514 are defined at each petal end by an apexfeature 516. In one example bending operation, as the deflectionaperture 513 begins to deflect an extruded length of wire 314 e, thewire 314 e may attempt to move or bend in an undesirable direction. Toassist in keeping the wire 314 e on track, the shape of the guidefeature 514 guides the wire 314 e into a more desirable location toachieve bending at a desired angle. In one embodiment, each petal 514can have a curvature with outer nadir 515 and a series of apex features516 separating the petals 514. Thus, during bending the wire 314 e iscaught with one of the guide features 514 (for example at a startingposition 540 wherein during the bending operation the wire 314 e slides(e.g., in direction 541) to a desired position 542. In particular, theapexes 516 can serve as restraining members (516) between the petals 514prevent free motion of the wire 314 e from petal to petal, therebyworking to restrain the radial motion of the wire 314 e as it is bent.This assists the deflector element 511 in correctly aligning the bentwire during use.

It is specifically pointed out that many different implementations ofsuch guide features can be used. For example, the inner surface of theaperture can comprise a set of slots or grooves in the inner surface toengage and fix the wire during wire bonding. In one exampleimplementation a series of notches can be arranged in a spaced apartarrangement around the inner surface of the aperture. For example, thespacing can be such that grooves are spaced every 5°, 4°, 3°, 2°, 1°, oreven tighter. It is pointed out that these intervals are examples onlyand that the invention is not limited to these intervals with those ofordinary skill appreciating that the spacing can be set at any desiredinterval. It is also pointed out, that alignment features can also bearranged on the capillaries. However, the inventors note that it isadvantageous to place them on the deflector element. This is because theformation of the guide features is time consuming and difficult.Additionally, the lifespan of an average capillary is considerably lessthan that of a deflector. Thus, although the invention contemplates theplacement of alignment features on the capillaries and/or the deflectorelement 511, there are certain advantages to placing them on the longerlived deflector element.

In a continuing description of the invention one method of applying thistechnology is described. In one embodiment, a method of employing a wirebonding apparatus 200 in accordance with an aspect of the invention isdescribed. This embodiment describes a wedge bonding method andassociated method of establishing wire bonds between bond sites. Anaspect of this invention will be discussed in association with theembodiment addressed in the flow diagram of FIG. 6.

Once the die (or other target subject) is positioned on the inventivewedge bonding tool bonding can begin. It is to be noted that appropriateadjustments and software instructions can be applied to the tool 200.

Accordingly, the distal end of a wire-bonding capillary is positionednear a first bonding site (Step 601). The capillary supports a bondingwire and can have an entire strand of appropriate wire in readiness fora bonding process. The wire can be of any material, with aluminum,copper, and even gold providing attractive materials. Aluminum inparticular provides some process advantages. In particular, aluminum issoft and also aluminum is compatible with many bond pad and bonding sitematerials (e.g., copper). Accordingly, it is not necessary to plate thetarget bond pads to obtain good bond adhesion between wire and pad as isthe case with some other materials (e.g., gold). Generally, suchpositioning involved positioning the capillary right above the bondsite. The capillary head must be positioned above the bond pad adistance that is thicker (e.g., 316) than the thickness (height) of theassociated deflector arm (e.g., 311). Thus, for a deflector arm 30 milsthick, the capillary head will be at least 35 mil and possibly muchhigher above the bond pad. In one example implementation the capillaryhead (the tip of the capillary) is positioned about 50 mils above thetarget surface (the bond site) in readiness for bonding. In general, thecapillary head is a distance above the bond pad that takes intoconsideration the height of the deflector above the bond pad, thethickness of the deflector, the thickness of the wire, and any desiredtolerances.

A length of wire is extruded from the aperture in the end of thecapillary (Step 603). In one implementation, a bond wire is fed downthrough an inner diameter of the capillary to extend a distance beyond afacing surface of the capillary. The extruded length can be on the orderof about the radius of the capillary face. Thus, for a capillary havinga diameter of about 6 mils, an extruded length of up to 3-4 mils can beused. It is pointed out that greater or shorter extruded lengths can beused. In particular, for greater diameter capillaries greater lengthscan be used and vice versa. As mentioned above, aluminum, copper, goldand other materials can be used with aluminum being a particularlyattractive candidate. Additionally, a wide range of wire thicknesses canbe employed with this methodology. One example range of wire thicknessescan include wire diameters ranging from about 5 μm to about 2 mils andother thicknesses. One example can be a 50 μm aluminum wire extruded toa length of about 3 mils using a capillary having a diameter of about 6mils. Of course this is but one example with many others apparent tothose of ordinary skill.

Once the desired length of wire is extruded, a movable deflector isimposed against the extruded length of bonding wire to bend the bondingwire to form a bent portion at an end of the bonding wire (Step 605). Adeflector (for example, a deflector 311 as is shown in FIGS. 4( a)-4(g))is brushed under the extruded portion of wire (for example, the wire 314e of FIGS. 4( a)-4(g)) bending the wire against the bottom face of thecapillary (for example, capillary 213 of FIGS. 4( a)-4(g)) to form thebent portion of the wire (for example, bent wire 403 of FIGS. 4(a)-4(g)). Importantly, as already discussed, the deflector bends thewire to attain the desired orientation (bond angle) relative to theassociated second bond site to which the wire is to be connected in thewire bonding process.

Additionally, the bending process requires that the deflector passbeneath the capillary. For example, in one embodiment the facing surfaceof the capillary can lie a distance of about 1.1 to about 1.5 wirediameters above the top surface of the deflector 311. Of course, thedistance can be less or greater. The general idea being that the desiredamount of bend is imparted to the bent portion of wire 403 by the motionof the deflector under the capillary.

Once bent, the deflector is repositioned such that the capillary canpass through the aperture of the deflector. Then the capillary is movedthrough the aperture toward the bonding site such that the bent portionof the bonding wire is moved into contact with the first bonding site(Step 607). Additionally, the facing surface of the capillary compressesthe bent portion of the bonding wire between the bonding site and afacing surface of the capillary to establish a wedge bond of the bondingwire with the first bonding site (Step 609). This process is typicallyenhanced using ultrasonic energy. For example ultrasonic bonding orscrubbing can enhance the bond between the wire and bonding surface.Also, in some embodiments thermosonic bonding can be used enhance thebond between the wire and bonding surface. This will be discussed insome detail below with respect to certain capillary heads. This processresults in a low temperature wedge bond that can be established in anydirection without need for changing the rotational orientation of thecapillary. This first novel aspect of this embodiment is completed inthe formation of this novel type of wedge bond.

Once the bond is established, the method can move the bonding wire to asecond bonding site to establish a completed wire bond electricalconnection with another circuit element. For example, the capillary ismoved away from the first bonding site (the location of the first bond)toward a second bonding site (where the bond that completes theconnection can be made) (Step 611). Once in the desired location thecapillary is positioned operative arrangement with the second bondingsite and the wire is wedge bonded to the second bonding site toestablish a wire bond connection between the first and second bondingsites (Step 613). A standard wedge bonding technique can be used hereand the wire can be broken off in a standard fashion to complete thebond. At this point the capillary can be removed to another bonding siteto repeat the process. Importantly, the rotational orientation of thecapillary is not changed in this move.

FIG. 7( a) is a cross-section view of one example of a capillary device213 suitable for use with some embodiments described in thisspecification. The capillary 213 can be made of any material. But whenused with aluminum wire, a hard material like aluminum oxide crystals(ruby, sapphire, etc.) can provide an excellent capillary material. Inaluminum applications such materials are harder than aluminum oxidematerials that sometimes form on bond wires. Such oxides are damaging toprior art ceramic capillaries. And such ruby materials also suffer fromless aluminum build up. Additionally, similar advantages can be obtainedwith tungsten carbide capillary materials. It is pointed out that thistechnology has applicability beyond aluminum wedge bonding and can beused with copper, gold, silvers, their alloys as well as various othermaterials. In addition to the materials described above, in someimplementations capillaries formed of ceramics (e.g., Zirconar ceramicand others) can also be used.

In one important attribute, the face surface 701 of the capillary isflat or very near flat. The face angle 702 (not drawn to scale) thatdescribes an angle that the facing surface 701 makes with a perfectlyflat plane should be less than about 4-5°. This very flat surfaceenables a maximum contact area of the surface 701 with the bent wire.Additional implementations can include faces with slight inverse angles(those having surfaces that become higher as they extend inward from theface edges). In general, these more flat surfaces are very differentfrom capillaries used to ball bond gold wires. Such ball bondingcapillaries are designed to optimize ball formation. Accordingly, theyhave relatively steep face angles. In a typical gold ball bondingapplication the face angle will be 8°, 12°, 15°, or even steeper. Thesetools cannot provide the needed contact area required to enable thepresent methodology. Additionally, when using gold processes, the facingsurface 701 is very smooth. However, in an aluminum bonding capillary, agreat deal of “scrubbing” is required to break up the surface oxidespresent on aluminum wires. Hence a rough surface is required. This isamplified through the effect of ultrasonic scrubbing. Such a roughenedmatte surface can be used with a ruby or tungsten carbide capillary.

It is also noted that a pattern of raised features can be used to goodeffect in this manner. For example a criss-crossed (cross-hatched)pattern of raised features (e.g., a waffle-shaped pattern) can providegood results. FIG. 7( b) is a side-section view of a facing surface 701having a number of raised features 703. Such a pattern is particularlyuseful when used with tungsten carbide capillaries. For example, in theembodiment shown, the pattern of features 703 can comprise a series ofridges that are spaced and sized at dimensions that are dependent on thediameter of wire used. For example, the ridges can be spaced a distanceabout 10-25% of the wire diameter, on center, and can have a height ofabout 10-25% of the wire diameter, width a ridge width of on the orderof about 4-15% of the wire diameter. For example, when applied to a 1mil wire, example features can include ridges spaced apart by about 0.20mils, with a height of about 0.20 mils, and being about 0.05 mils wide.It will be readily appreciated that smaller feature dimensions as wellas larger can be used.

In another embodiment, FIGS. 7( c) and 7(d) depict a facing surface(e.g., 701) of another capillary 713 facing surface 701. The facingsurface 701 includes a series of guide features formed in the facingsurface 701. As shown here, the guide features comprise positioninggrooves 711 arranged in the facing surface 701. The grooves 711 areconfigured to aid in the position of bonding wires as the wired willslide into the grooves during bonding making the wire positioning moresecure and precise. In the depicted embodiment, the grooves 711 arearranged like spokes around a centralized aperture 714 through which theextruded wire is supplied for wire bonding. Depending on the needs ofthe user more (or less) spokes can be employed.

Referring to side section view of FIG. 7( d), the seating grooves can beconfigured having shallow or deep depths. Preferred embodiments arearranged with the depth of seating grooves 711 being in the range ofabout 25-405 of the thickness of the wire used. In one example, a 15 μmwire can have a groove 711 depth of on the order of about 5 μm. The ideabeing that a wire will slide into the groove, during bonding, andprevented from further substantial radial movement once lodged in thegroove 711. As for the remaining portions of the surface, they can besmooth or roughened depending on the needs of the user.

Returning to a discussion of FIG. 7( a), the outer edges 704 of thecapillary are also different from known geometries. This difference isintended to provide a larger surface area for contacting the wire. Thus,a radius of curvature for the outer edge 704 of the capillary is muchless than that used for a gold ball bonder. For example, in the presentinvention, the radius of curvature for the outer edge 704 is on theorder of 12 μm or less. This, radius is very small as compared with the20 μm or greater radii commonly found in gold ball bonding capillaries.

Additionally, the chamfer angle in the present capillary is steeper thanthat of an ordinary ball bond capillary. This can be characterized bythe interior chamfer angle (ICA) depicted in FIG. 7( a) as ICA 704. In asuitable embodiment used for the wedge bonding applications describedhere, angles in the range of about 0° to about 120° can be suitable.With angles of 70° of less being preferred in some implementations. Thisenables a tighter chamfer and thereby increases the surface area of thefacing surface 701. In this application, a chamfer diameter 705 is about1.5 times the diameter of the bond wire used. Additionally, the borediameter 706 is sized to be in the range of about 6-10 μm more than thediameter of the bond wire used. However, in some implementations theouter chamfer diameter 705 may be arranged only slightly larger or ofthe same diameter as that of the bore 706. Another feature is a borelength 707 that defines a length of the bore shaft that is verticalwalled to enable the wire to remain straight as the deflector bends thewire. In one implementation this is one the order of about 1-2× the bondwire diameter. It is pointed out that this is just one exampleimplementation and is not the only way such a capillary can be formed.In one embodiment, it is important that the facing surface be flat (ornearly so), that the facing surface have a roughened or patternedsurface rather than a smooth face, and that the facing surface begenerally round (a typical facing surface being shown for 213 in FIG.3).

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the present inventionare presented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed. It will be apparent to one of ordinary skill in the art thatmany modifications and variations are possible in view of the aboveteachings.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

1. A wire bonding apparatus comprising: a support for holding wirebonding substrates; a wire bonding capillary with an aperture forcarrying and extruding bond wire and enabling bond wire attachment towire bonding substrates; a movable deflector element arranged to movegenerally adjacent to a facing surface of the capillary to bend anextruded length of bonding wire such that the bent extruded length ofbonding wire can be articulated at different bond line angles whilemaintaining a constant rotational orientation for the capillary; whereinthe movable deflector element having an aperture comprising a centerwith an inner surface of the aperture arranged concentrically about thecenter further including a plurality of wire guide features to assistpositioning of the extruded length of bonding wire wherein a first wireguide feature comprises a recessed portion that lies a greater radialdistance from the center of the aperture than a remaining portion of theinner surface of the aperture; and wherein the capillary comprises afacing surface that includes at least one of a roughened matte surfacearranged on the facing surface, a pattern of intersecting ridges forminga criss-crossed pattern arranged on the facing surface, and a series ofridges arranged on the facing surface; and a controller configured toenable control the operation of the wire bonding apparatus.
 2. The wirebonding apparatus recited in claim 1 wherein the movable deflectorelement further comprises a deflector aperture having an inner surfacesized so that the wire bonding capillary can pass through the apertureof the movable deflector element; and wherein said first wire guidefeature is arranged on the inner surface of the deflector aperture. 3.The wire bonding apparatus of claim 2 wherein the first wire guidefeature and a capillary wire guide feature cooperatively interact withthe extruded length of bond wire to assist positioning of the extrudedlength of bonding wire.
 4. The wire bonding apparatus of claim 2 whereinthe capillary facing surface comprises the pattern of intersectingridges forming the criss-crossed pattern arranged on the capillaryfacing surface.
 5. The wire bonding apparatus of claim 2 wherein thecapillary facing surface comprises the series of ridges arranged on thefacing surface arranged on the capillary facing surface.
 6. The wirebonding apparatus of claim 1 wherein, the movable deflector elementmoves generally horizontally across the facing surface of the capillaryto bend the wire so that the bent extruded length of bonding wireextends substantially parallel to a plane of the facing surface of thecapillary.
 7. The wire bonding apparatus of claim 1 wherein, the wirebonding capillary and the movable deflector element are arranged toenable the capillary to move downward through the aperture in themovable deflector element to contact the bent extruded length of bondingwire with a bonding site of a wire bonding substrate positioned on thesupport.
 8. The wire bonding apparatus of claim 7 wherein the apparatusincludes an x,y motorized table controllable by the controller andconfigured to move the deflector element such that the bent extrudedlength of bonding wire is articulated in a pattern of predetermined bondline angles.
 9. The wire bonding apparatus of claim 1 wherein thecapillary facing surface is configured to compress the bent extrudedlength of bonding wire between a bonding site of the wire bondingsubstrate and the facing surface as the capillary compresses the bentextruded length of bonding wire between the bonding site and thecapillary facing surface.
 10. The wire bonding apparatus of claim 1wherein the capillary is arranged to compress the bent extruded lengthof bonding wire between the bonding site and a capillary wire guidefeature during wedge bonding.
 11. The wire bonding apparatus of claim 10wherein the capillary facing surface is substantially flat having anangle from the horizontal of in the range of about 0° to about 4°. 12.The wire bonding apparatus of claim 1 wherein the capillary facingsurface comprises the matte surface arranged on the facing surface. 13.The wire bonding apparatus of claim 1 wherein the apparatus enables abonding rate of at least five bonds per second.
 14. The wire bondingapparatus of claim 1 wherein the apparatus enables a bonding rate of atleast twelve bonds per second.
 15. The wire bonding apparatus of claim 1wherein the apparatus further includes an ultrasonic bonding module forenabling ultrasonic bonding of the bent extruded length of bonding wirewith the bonding site.
 16. The wire bonding apparatus of claim 1 whereinthe capillary facing surface comprises the pattern of intersectingridges forming the criss-crossed pattern arranged on the capillaryfacing surface.
 17. The wire bonding apparatus of claim 1 wherein thecapillary facing surface comprises the series of ridges arranged on thefacing surface arranged on the capillary facing surface.